Process of production of an acid magnesium-sulfite solution.u



JAMES LOC'I. IABDINE, OF PENIGUIIK, SCOTLAND.

EROCESS 0F PRODUCTION OF AN ACID MAGNESIUM-SULFITE SOLUTIUN.

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No Drawing.

To all whom it may concern:

Be it known that I, Jams LOGKHART JAR- DINE, a subject of the King of Great Britain and Ireland, and a resident of Penicuik, in the county of Midlothian, Scotland, have invented a certain new and useful Improved Process of Production of an Acid Magnesium-Sulfite Solution, of which the following is the specification. 7

It is essential when preparing a bisulfite solution for wood resolution to take special precaution to keep the water which is associated with the base and into which the S0 gas is conveyed as cold as possible, as its temperature has considerable influence on the amount of sulfur dioxid which can be absorbed. So vitally important is it to keep the temperature low, that resort is sometimes made to artificial cooling by refrigeration, the aim being to secure a liquid with a high percentage of free or available $0,. In other words, the sulfur dioxid is simply dissolved in Water, so forming sulfurous acid, and a common analysis of the prepared liquor shows 4% to 5% of total 50,, and of this only 1% is combined with the base. In contrast to this, a liquor suitable for the extraction of easily bleachable cellulose from bamboo and like vegetable materials having mixed lignin and pectic constituents need not contain even the bisulfite proportions of acid, provided a suflicient quantity of the base can be brought into solution.

At low temperatures, although. water rapidly absorbs SO to form sulfurous acid, this acid dissolves magnesia very slowly, and its degree of l /lgSO saturation is low, and thus at ordinary temperatures it is necessary to add at least the bisulfite proportion of 50 to bring the required quantity of the base into solution. If, however, the water in which the MgO is suspended be heated, the rapidity of base solution is greatly increased, and a larger percentage can be dissolved and held in solution.

The approximate MgSO saturation points of slightly SO, acidulated water range from 0.2% at 50 F. to 2.34% at 160 F. and the rate of progression between these points is regular. At the higher temperatures when the MgSO saturation point is Patented July 25, 1936..

Application filed January 29, 1916. Serial No. 75,048.

reached and there is still MgO in suspension, thls by the continued addition of SO combines and separates as crystals of MgSO but these are again dissolved when they take up the second equivalent of SO to form the bisulfite.

It will be seen from the foregoing that the I higher the temperature the less S0 is required to effect the solution of the base, and that if a known percentage of magnesia be present in the water, it is easy to calculate what quantity'of S0 must be added to secure its solution at any temperature. For example, it is desired to make an acid sulfite solution which has dissolved in it 1% of MgO and having two thirds of its SO contents combined and one third free or available. A saturation curve plotted from the aforegiven figures shows that at 110 F. 1.3% of MgSO can be carried in solution. This is composed, according to atomic weights, of 0.8% S0 and 0.5% of MgO; thus half the required base will have been dissolved by the addition of 0.8% S0 but saturation point has been reached, and consequently the second half of the base needs the double SO addition, viz :-1.6%, as before solution can be insured'it must be converted into the bisulfite.

If the temperature be maintained at or' over 110 F. when (by the ordinary analysis) the liquor shows that 2.4% SO has been added, it will be found that 1.6% will be combined and 0.8% will be available or free, 2'. 6. held in loose combination as the bisulfite but commonly spoken of as free.

In carrying out this process any of the known types of milk of lime apparatus can be employed. Well calcined magnesium oXid in a powdered form is the base used, and it is by agitation kept suspended 1n water which hasbeen previously heated to the desired temperature, or the heating can be gradually effected by the application of the hot or partially cooled S0 gas generated in an ordinary type of sulfur burner.

On its way to the absorption or liquor making apparatus the gas is passed through a series of water cooled lead pipes, and, by varying the'water supply or area exposed, the temperature of the gas may be controlled and regulated, and this may be made the means of maintaining the liquor throughout all the stages of its production at the required temperature, thereby insuring that known and predetermined proportions of combined and free SO can be secured when the liquor reaches a fixed total SO strength. By this means, advantage is taken of the heat of the gas to raise the liquor temperature, and by controlling it, the degree of MgSO saturation can be varied. By the said heating, the direct and rapid solvent powers of the S0 are further enhanced, and thus an acid sulfite solution containing the percentage of base and S0 suitable for the vegetable tissue to be treated may conveniently be made; it being understood that the greater the proportion of pectic ingredients which the material contains, the larger the percentage of base must be provided, and conversely, if lignin preponderates, more S0 and less base must be provided in the resolving solution. 1

It will be readily seen that this process may be successfully and economically carried out in hot climates, and this is a very important feature, as a large number of the vegetable growths from which cellulose can be extracted are indigenous to the tropics.

In the specification of the prior Patent No. 1,143,401 of 1915, there is described a process for cellulose extraction from bamboo and the like. Therein is specified a magnesium bisulfite solution, and is arranged means for the relief and removal of the gasified'SO so in elfect there is provided gradually throughout the cooking process a solution containing less than the bisulfite proportion of S0,, with the result that the acid action of the bisulfiteis very mild, and thus the basic part of the salt throughout the process is free to co-act, so insuring that thenon-cellulose ingredients of the vegetable tissue are successfully extracted and retained in solution. By the means described in the first part of this specification,

there may now be prepared a solution co n. tainlng therequisite proportions, of dissolved base and free S0 and it.may be modified to suit any vegetable substance of mixed lignin. and pectic properties. Thisprocess, as has already been shown, can be so controlled that the required proportion of base is present without excess of S0 and thus practically none will be gasified, and while it is being used in the cooking process, no arrangement need be made for relief or recovery.

In order to make clear the details of the action and application of a solution of this nature, particulars regarding the method of securing paper-makingpulp from bamboo arundinacea as grown in southern India are now given. The disintegrated culms are cut and packed into a suitable digester and covered with a magnesium acid sulfiteliquoi' I having the following analysis:2.4% total S0,, 1.6% combined, and 0.8% free or available. All the S0 contained in this solution is required for the satisfactory chemical resolution, and as the base and fibrous tissue of cooking assists in maintaining the proper circulation of the liquor. The full pressure of 85 to 90 lbs.'per square inch above atmosphere is reached in two or three hours,

. and the cooking is thereafter generally completed in eight to nine hours, the stages of resolution and terminal point being determined by analysis of the liquor as described in Patent No. 1,143,401 of 1915. It is to be noted that when using this process there is in the first stages of the cook an insufficiency of free or available SO t0 sulfonate the lignin, and although same may be separated from the fiber by the solution of the pectic substances, its ultimate solution depends upon the liberation of the S0 originally combined as the sulfite, and thus it is at the final stages of the resolution before all the separated ingredients are brought into solution.

When there is a slight shortage of S0 although the incrusting or intercellular mat- .ters may be fairly well separated, they are acid magnesium-sulfite solution for the extraction of cellulose from fibrous vegetable materials, which consists in maintaining the liquor at such temperature during the formation of the solution that there is dissolved by the S0 that desired greater proportion of the base than is dissolved at normal temperature.

2. A process for the production of an acid magnesium-sulfite solution for the extraction of cellulose from fibrous vegetable materials, which consists in dissolving the base in the liquor at a temperature above F. and in the presence of sulfur dioxid.

3. A process for the production of an acid magnesium-sulfite solution for the extraction of cellulose from fibrous vegetable maname to this specification, in the presence of terials, which consists in subjecting a sustwo subscribing witnesses. pension of magnesium oXid to the action of hot sulfur dioxid to raise the temperature JAMES LOOKHART JARDINE' 5 of the liquor above 70 F., for thepurpose Witnesses:

set forth. DAVID FERGUSON,

In testimony whereof I have signed my JAMEs EAGLESOM. 

